All we have to believe with is our senses: the tools we use to perceive the world, our sight, our touch, our memory. If they lie to us, then nothing can be trusted. And even if we do not believe, then still we cannot travel in any other way than the road our senses show us; and we must walk that road to the end.
(from American Gods by Neil Gaiman)
What happens when that road our senses show us is a dead-end?